Robotic Gripper Made from Coffee-Filled Balloon Picks Up Anything

As robot hands go, this is the weirdest I've ever seen. But you know what? It works really well.

Researchers at Cornell University, University of Chicago, and iRobot reported this week that they've developed a fingerless robotic gripper made from a rubber bag filled with coffee grounds.

The gripper can transition from a soft state, when it's easily deformable and can conform to the shape of various objects, to a rigid state, when it can firmly hold the objects.

The secret, the researchers report in a paper published in the Proceedings of the National Academy of Sciences (PNAS), is the "jamming" phase transition of granular materials -- in this case, coffee grounds.

The approach, they write, "opens up new possibilities for the design of simple, yet highly adaptive systems that excel at fast gripping of complex objects.” 

Researchers have used the "jamming" principle for robot locomotion before, but this appears to be the first application in manipulation.

So how does it work? When a granular material like sand or coffee grounds is loosely packed it can flow almost like a liquid. But when the particles in the material are packed tightly together, they "jam," or lock into one another.

One way of jamming them together is by applying a vacuum. You've seen it before: Vacuum-sealed coffee packages are hard bricks, but when opened, air rushes in and the packages become deformable.

The gripper is a clever idea. Now, is it practical? How strong is it? And can this coffee-powered robot hand fetch you a cup of coffee?

To find out more, I spoke to Eric Brown, the lead author of the PNAS paper and a postdoc at the laboratory led by Prof. Heinrich M. Jaeger at the University of Chicago.

The other authors are Nicholas Rodenberg and Prof. Jaeger from the University of Chicago; John Amend and Hod Lipson from the Cornell Computational Synthesis Laboratory, in Ithaca, N.Y.; Annan Mozeika and Erik Steltz from iRobot, in Bedford, Mass.; and Mitchell R. Zakin from the U.S. Defense Advanced Research Projects Agency, in Arlington, Va.

Erico Guizzo: This is an unusual gripper approach and I was wondering how the idea came about.

Eric Brown: This grew out of a program to develop a new field of soft robotics that was sponsored by DARPA. It was based on the observation that humans and animals are mostly made of soft materials, but robots have usually been made of hard materials like metal, and maybe we could build robots with more of the functionality of humans if we switched to softer materials. My group at the University of Chicago had experience in the physics of soft and granular materials, and we were paired up with robot engineers at Cornell and iRobot. My group has been studying a transition between soft and hard states of granular materials, called "jamming", and together we decided that gripping was a good robotics application for this.

EG: You successfully tested the gripper with varied objects -- what's the one object you were most surprised it could hold? And is there anything that it failed to hold?

EB: I think I was most surprised that it was able to pick up a penny, because we had expected it would have a harder time forming around very flat objects. We were especially excited that it could pick up fragile objects like raw eggs and wine glasses, because these are traditionally challenging for robotic grippers. It doesn't do well with extremely soft objects like cotton balls.

EG: How strong is the gripper? That is, how much weight can it lift, and once it's holding something, how strong is the grasp?

EB: The heaviest objects we lifted with the hand-sized gripper were a pair of gallon jugs of water, weighing a total of about 15 pounds [6.8 kilograms]. The grip is easily strong enough to lift and hold onto anything that fits into your hand, and can hold on, for example, if something bumped into it. However, you could pull something out of the grip with your own hand. The technology is scalable, so we predict that with a larger gripper, about 3 feet across [0.9 meters], would be able to lift up a car.

EG: One of the press materials states that the gripper could "outperform robotic fingers when confronted with unfamiliar objects or complex shapes" -- could you give a few actual examples?

EB: We never did direct comparison tests against other grippers. The argument behind this statement is that the gripper can pick up a variety of different objects, and quickly, because the granular material will conform to the shapes of the objects. Even very robust robotic hands with fingers need to spend extra time to examine the object and calculate optimal positioning for each finger, things that our
gripper doesn't need to spend time doing.

EG: This mechanism of soft-to-rigid transformation -- was it a well-understood phenomenon? Did anyone try to exploit it before?

EB: People have understood that soft pads on fingers or pincers give a little more tolerance so we can pick up things that have unusual shapes or are fragile, such as a wine glass, without breaking them. While people had proposed the idea of using granular materials in bags for these soft pads, no one even bothered to try it out because they didn't think it would be more advantageous that a piece of soft rubber. What they had not thought of was that you could use the jamming transition could do the pinching as well, eliminating the need for individual fingers or pincers.

Video and more photos:

Photos: John Amend/Cornell University

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